Wear indicator system for offshore corrosion protection covering systems

ABSTRACT

A corrosion protected metal pipe for installation in an offshore structure or for producing a pipeline laid in water is provided. The metal pipe has an at least two-layer covering on the pipe with a lower layer facing the pipe and an upper layer on a side of the lower layer not facing the pipe is provided. The layers are formed such that the lower layer is electrically conductive and the upper layer is electrically insulating, the lower layer is optically contrasting to the upper layer, or the lower layer is electrically conducting and optically contrasting to the upper layer and the upper layer is electrically insulating. Thus, in the event of damage to the layer or layers lying above, a visual or electrical signal can be detected. Damage to the corrosion protection covering can therefore be detected easily and, if appropriate, reported by remote monitoring.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is continuation application of U.S. application Ser.No. 13/872,207, filed on Apr. 29, 2013, and claims priority to GermanApplication No. 102012207179.2, filed Apr. 30, 2012, the disclosure ofwhich is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

The invention relates to a wear indicator system for metal pipes whichare part of an offshore structure or a pipeline and are covered with acorrosion protection system.

Offshore structure designates stationary structures which are erected inthe open sea off the coast. Examples of such offshore structures arewind power plants, drilling rigs and lighthouses. The pipelines inquestion are rigid pipes having a solid metal wall, as opposed toflexible pipes of multilayer construction.

The metal pipes are, for example, part of the foundation structure ofoffshore structures. The foundation structure of offshore structures isthe area which carries the actual functional unit. In the case of windpower plants, the foundation structure carries the tower includingturbine and rotors. In the case of drilling rigs, the foundationstructure carries the platform including superstructures. In the case oflighthouses, the foundation structure carries the tower, if present, andthe light. The foundation structure lies underwater, in the intertidalzone, in the foam zone and possibly in the aerosol zone. The foundationstructure includes the foundation elements with which it is anchored inthe sea floor.

In the course of the planned expansion of wind power utilization, alarge number of offshore wind power plants are planned for the comingyears both in the North Sea and in other seas and in inland seas. Theoverall mechanical system of an offshore wind power plant comprises thecomponents turbine, rotors, tower and foundation structure.

In order to base these plants on the bottom of the body of water, atlocations up to over 100 km from the coast, specific constructions arerequired, which differ highly from the constructions in the onshoreregion. Some regions of these complicated constructions, such asmonopiles, jackets, tripods, tripiles, etc., are subjected to highstatic and primarily dynamic and corrosive loading. Depending on theposition and water depth at the respectively considered location, whatare known as the 50-year wave and the tidal range have to be taken intoaccount. Added to this are high UV radiation, salty spray, foam,aerosols, temperature changes, mechanical loadings, growth with musselsand other life forms and associated mechanical wear by animals andchemical ablation as a result of discharges from animals and othermarine life forms. For these constructions, use is made of steel pipeswhich, for corrosion protection reasons, can be sealed off in anairtight manner or filled with concrete. Furthermore, power or othersupply lines can run through the steel construction pipes.

To date, the metal pipes needed for the construction have been designedwith substantially thicker wall thicknesses (up to 25%) than directlynecessary and conventional paints, mostly based on epoxy resin orpolyurethane, are used for the corrosion protection. As a rule, thesepaint systems do not offer particular protection against mechanicalloading. In addition, these frequently have to be applied by hand atgreat heights, which results in quality control being difficult. Thequality of such a coating is not comparable with the coating performedat the factory.

EP 2 511 430 describes that steel construction pipes which are coveredwith an extruded layer made of a polyamide moulding compound can be usedin the foundation structure of offshore structures. Better protectionagainst mechanical loadings and against corrosion and UV irradiation isachieved therewith than in the case of the previously known applicablepipes. The covering can also be formed in multiple layers.

Pipelines made of metal are currently frequently covered with apolyolefin such as polyethylene or polypropylene (WO 2002/094922; US2002/0066491; EP-A-0 346 101). The coatings or coverings are usedprimarily for corrosion protection; they are described by correspondingstandards. For the polyolefin covering, these are, for example, DIN EN10288 and DIN 30678. In the case of the polyolefin covering, this layeris produced, for example, by means of tubular or wrapping extrusion. Forthe purpose of adhesion promotion, epoxy and adhesive layers can beapplied one after another before the extrusion.

Conventionally, as regulated by DIN EN 10310 (German version EN10310:2003), steel pipes for underground and water-laid pipelines arecoated by means of polyamide powder. The polyamide coating is applied bydipping in a fluid bed, spraying on or in the roll application process.Because of the process, only relatively thin layers can be applied tothe metal by means of powder coating. Disadvantageous in particular isthe fact that a powder made of a relatively low-molecular weightpolyamide has to be used for the coating, in order to ensure good flowof the melt on the hot metal surface. A coating obtained in this way isprimarily used for corrosion protection. Furthermore, thermosettingcoatings based on epoxy or polyurethane are also known.

In pipeline construction, higher technical requirements are to anincreasing extent being placed on the pipe coating, since theenvironmental, laying and operating conditions are becoming more andmore demanding. One of the most effective methods to protect undergroundpipelines against corrosion, in particular in the case of cathodiccorrosion protection, is a multilayer covering. This consists of anepoxy resin layer as a first layer, a copolymer as adhesive as a secondlayer and an outer polyolefin layer made of polyethylene orpolypropylene. This covering method can be applied to pipes from smallto large. However, in the offshore and onshore area, high requirementsare often additionally placed on the resistance against mechanicalstresses. In order to take this problem into account as well,WO2010/094528 recommends the use of a metallic conduit pipe which iscovered with an extruded layer made of a polyamide moulding compound, toproduce a pipeline laid in water.

Damage to such corrosion protection coatings leads to the corrosion ofthe steel construction to be protected and can thus lead to structuralendangering of the structure or the pipeline. Conventional procedures,therefore, firstly, primarily in offshore structures, include regularon-site inspection of the corrosion protection; secondly, the steelconstruction is designed with the inclusion of a safety factor whichpermits time-limited corrosion of the steel construction caused bydamaged protective layers.

Since, for example, offshore wind power plants are not continuouslyoccupied, the inspection of these wind power plants is associated withconsiderably increased expenditure; a visit to the plant is alwaysnecessary. As a result of external influences of the weather and of thesea, a visit or visual inspection of the plant is not always possible,however, which additionally makes the inspection more difficult.

The object of the invention is, therefore, to develop a wear indicatorsystem for corrosion protection covering systems which, even in the caseof non-regular occupancy of offshore structures, permits reliableassessment of the corrosion protection. In particular, travelling tothese structures should therefore be limited to a minimum and, inaddition, the safety margin in designing these structures can bereduced.

SUMMARY OF THE INVENTION

This and other objects have been achieved by the present invention thefirst embodiment of which includes a corrosion protected metal pipe,comprising:

a metal pipe; and

an at least two-layer covering on the pipe having a lower layer facingthe pipe and an upper layer on a side of the lower layer not facing thepipe;

wherein

the lower layer is electrically conductive and the upper layer iselectrically insulating,

the lower layer is optically contrasting to the upper layer, or

the lower layer is electrically conducting and optically contrasting tothe upper layer and the upper layer is electrically insulating.

In a further embodiment of the present invention, the upper and thelower layer each, independently, comprise a polymer material and in anaspect of this embodiment, the upper layer is a polyamide mouldingcompound applied by extrusion.

In another embodiment of the present invention at least one furtherlayer is between the metal surface and the lower layer and the at leastone layer between the metal surface and the lower layer is selected fromthe group consisting of a ceramic layer, a priming layer, an adhesionpromoting layer and a textile reinforcement.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a protected pipe structure according to one embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

The object described above has been achieved by a metal pipe which hasan at least two-layer corrosion protection covering with an upper and alower layer, the lower layer being finished such that, in the event ofdamage to the layer or layers lying above, a visual or electrical signalcan be detected. Thus the metal pipe is covered with an at leasttwo-layer covering having a lower layer facing the pipe and an upperlayer on a side of the lower layer not facing the pipe; wherein thelower layer is electrically conductive and the upper layer iselectrically insulating, the lower layer is optically contrasting to theupper layer, or the lower layer is electrically conducting and opticallycontrasting to the upper layer and the upper layer is electricallyinsulating.

The present invention also includes the use of the corrosion protectedmetal pipe for installation in an offshore structure, in particular inthe foundation structure of an offshore structure, or for producing apipeline laid in water.

In a first embodiment, the lower layer, which is the layer facing themetal of the pipe, is designed to be electrically conductive, while theupper layer, facing the water, is designed to be electricallyinsulating. By application of an electric voltage with respect to thewater, it may thus possible to detect damage to the coating by means ofremote monitoring, as a result of the short circuit that then occurs.The water is preferably water which contains dissolved salts, forexample seawater or brackish water. The electrically conductive layermay be insulated with respect to the metal. However, it may also beconductively connected to the metal, so that the metal construction isat the same potential.

In a second embodiment of the present invention, the two layers lyingone above the other are constituted in an optically contrasting manner.In general, they differ in colour. If, for example, the upper layer isset to be yellow and the lower layer red, then damage to the upper layermay be detected by means of the occurrence of red areas. The contrastpreferably corresponds at least to the grey scale rating of 4 (accordingto DIN EN 20105-A02), particularly preferably at least to the grey scalerating of 3 and in particular preferably at least to the grey scalerating of 2/3. The measurement may be carried out in accordance with DINEN ISO 11664-4, using a spectrophotometer (sphere).

In a third possible embodiment of the present invention, the first andthe second embodiments are combined with each other. Damage may then bedetected by means of the occurrence of a short circuit and reported byremote monitoring; on-site, the damage may then be found and repairedquickly by the optical contrast. This principle is illustrated in FIG.1.

In FIG. 1, a steel pipe with concrete filling is illustrated, which hasbeen covered with a layer made of an electrically conductive plastic andthereafter with a layer made of an electrically insulating plastic. Thetwo plastic materials are coloured differently. The outer, electricallyinsulating covering layer has been damaged at a point, so that theelectrically conductive layer comes into contact with seawater. As aresult, a short circuit is detected via an electric resistancemeasurement. The damaged point may be found by locating the opticalcontrast on the pipe.

The electrical conductivity of the lower layer may be obtained by any ofconventionally known methods, for example, by using a moulding compoundfilled with conductive carbon black or by embedding axially extending orwound electric conductors, for example wires, stranded wires or tapes.

The offshore structure may preferably be an offshore wind power plant, adrilling rig or a lighthouse.

The foundation structure of an offshore wind power plant is thestructure which carries the tower. It extends from the foundationelements, which are anchored in the sea floor, via the structure whichis located underwater, as far as the point at which the tower begins andwhich may be located above the calm water level.

The following types, for example, are used as the foundation structure:

The monopile construction comprises a cylindrical hollow pile. Themonopile is used close to the coast in many European offshore windparks; it is suitable for foundations at water depths of up to currentlyabout 20 meters. Monopiles can be installed simply and quickly; however,heavy pile driving equipment is needed for the erection. In recenttimes, trials of a gentle installation using a drill head have beencarried out.

The jacket is a latticework construction made of steel which resemblesthe construction of conventional power masts. At its four feet, thejacket is anchored in the sea floor with piles. The jacket constructionhas already proven worthwhile in the oil industry at relatively greatwater depths. As a result of the latticework construction, 40 to 50%steel can be saved as compared with the monopile. Thus, the projectcosts when this construction is used at relatively great water depthsincrease only relatively slightly. Since the individual structuralelements are relatively small, they can be produced easily and can betransported and mounted simply.

In the case of the tripod, the structure comprises a tripod formed fromsteel pipes, on which the central pipe is placed centrally. The legs ofthe tripod can each be seated on a pile or on a plurality thereof. Inorder to drive the pile, centring sleeves are arranged at the cornerpoints of the equilateral triangle that results. The piles are connectedto one another by horizontal struts and connected to the central pipevia diagonal bracing. The central pipe does not enter the sea floor.Since steel pipes having smaller diameters are used in this case, thetripod can be used for water depths of more than 20 meters.

The quadropod is a modification of the tripod concept with four insteadof three struts. In this case, increased foundation rigidity is achievedat great water depths.

The tripile comprises three steel piles, which are anchored under water.Above water, a tripod construction is placed on these steel piles.According to manufacturer's information, tripile foundations aresuitable for water depths of 25 to 50 meters.

Constructions of this type are described, for example, in the followingpublications:

-   Fundamente für Offshore-Windenergieanlagen [Foundations for Offshore    Wind Power Plants], Deutsche Energie-Agentur GmbH, as at 12/09;-   Florian Biehl, Kollisionssicherheit von Offshore-Windenergieanlagen    [Collision Safety of Offshore Wind Power Plants], Stahlbau, Vol. 78    (6), pp. 402-409 (2009);-   K. Lesny, W. Richwien (Publishers), Gründung von    Offshore-Windenergieanlagen-Werkzeuge für Planung and Bemessung    [Foundations of Offshore Wind Power Plants—Tools for Planning and    Dimensioning], VGE Verlag Glückauf 2008, ISBN: 978-3-86797-035-8;-   DE 103 10 708 A1.

The upper and the lower layers of the corrosion protection coveringaccording to the present invention may be of a polymer material, forexample a polyamide moulding compound, a polyolefin moulding compound, afluoropolymer moulding compound (for example based on PVDF), a mouldingcompound based on a thermoplastic polyurethane, a cross-linkedpolyurethane or a cross-linked epoxy resin.

In a preferred embodiment, the upper layer is a polyamide mouldingcompound applied by extrusion. The lower layer may then either likewisebe a polyamide moulding compound, a polyolefin moulding compound oranother polymer material. The material of this lower layer may containan adhesive resin, for example epoxy resin (for example Araldite®); inthis case, this layer can be applied directly to the metal surface.

In general, however, between the metal surface and the lower layer theremay be at least one further layer. For example, this at least onefurther layer may involve one or more of the following layers:

-   -   a ceramic layer, for example, such as described in WO 03/093374;    -   a priming layer, for example of epoxy resin (U.S. Pat. No.        5,580,659) or a water-based mixture of epoxy resin and        polyacrylate latex (WO 00/04106);    -   an adhesion promoter layer made of a polyamide hot-melt adhesive        which, for example, can be applied as powder by spraying, etc.        (EP 1 808 468 A2), or of a polyolefin which bears functional        groups. Suitable functional groups are, for example, carboxyl        groups or acid anhydride groups (WO 02/094922), epoxy groups or        alkoxysilane groups (EP-A-0 346 101). The polyolefin layer may        also be foamed. The polyolefin may preferably be polyethylene or        polypropylene;    -   a differently composed adhesion promoter, which is intended to        ensure that the composite comprising polyamide layer and base        material is not impaired under mechanical stress;    -   a textile reinforcement in the form of woven fabrics or mats,        for example made of glass fibres or aramid fibres (Kevlar).

The optional ceramic layer, priming layer, adhesion promoter layerand/or textile reinforcement may be applied to the pipe in accordancewith any conventionally known method.

The materials of the upper and lower layer may be applied to the pipe inaccordance with methods which are conventionally known, for example bymeans of tubular or wrapping extrusion. In one possible variant, bothlayers, possibly together with an adhesion promoter layer, may beproduced and applied by means of co-extrusion of a multilayer composite.

The tubular and the wrapping extrusion are covering methods that haveproven worthwhile over a long time for pipes. These methods aredescribed in more detail in the Stahlrohr-Handbuch [Steel PipeHandbook], 12th edition, pp. 392-409, Vulkan-Verlag Essen, 1995.

The applied layers must be at least so thick that they can be producedas a closed layer under the application conditions. The layer thicknessmay preferably be at least 0.5 mm, particularly preferably at least 1.0mm and in particular preferably at least 1.2 mm.

Usually, layer thicknesses up to about 8 mm, preferably up to about 7mm, particularly preferably up to about 6 mm and in particularpreferably up to about 5 mm have proven worthwhile. If required,however, the layer may be thicker, for example up to 30 mm or more.

The metal pipe may be steel, stainless steel, copper, aluminium, castiron, zinc, alloys with one of these metals as main component, brass,galvanized steel, cadmium-coated steel, aluminium-coated metal, steelcoated with metal alloys, such as GALFAN, or of any other metal. Thepipe may be produced by all conventional methods, including for example,as welded or seamless pipe.

The outer diameter of the metal pipe may preferably be at least 20 mmand at most 8000 mm.

The individual pipes are connected to one another constructionally byconventionally known methods, for example, by welding.

A particular advantage of the invention is that the damage may bedetected and repaired when the metal construction itself has not yetbegun to corrode. In this case, the repair may be considerably lesscomplicated overall.

Numerous modifications and variations of the present invention arepossible in light of the above description. It is therefore to beunderstood that within the scope of the appended claims, the inventioncan be practiced otherwise than as specifically described herein.

The invention claimed is:
 1. A method of determining corrosion of aninstalled cover metal pipe, the method comprising: performing aninspection for corrosion of the installed covered metal pipe, whichcomprises a metal pipe with an outer at least two-layer covering and isat least partially submerged in water comprising salt, via the at leasttwo-layer covering operable as a corrosion detector, wherein the atleast two-layer covering includes a lower layer facing the metal pipeand an upper layer on a side of the lower layer not facing the pipe; andwherein the lower layer is electrically conductive and the upper layeris electrically insulating, the lower layer is optically contrasting tothe upper layer, or the lower layer is electrically conducting andoptically contrasting to the upper layer and the upper layer iselectrically insulating.
 2. The method according to claim 1, wherein thelower layer is electrically conductive and the upper layer iselectrically insulating.
 3. The method according to claim 2, wherein thelower layer comprises an electrically conductive material.
 4. The methodaccording to claim 3, wherein the electrically conductive material isselected from the group consisting of conductive carbon black, anaxially extending conductive wire or tape and a wound conducting wire ortape.
 5. The method according to claim 2, wherein said performing iscarried out by applying an electric voltage to the electricallyconductive lower layer with respect to the water and detecting anelectrical signal.
 6. The method according to claim 1, wherein the lowerlayer is optically contrasting to the upper layer.
 7. The methodaccording to claim 6, wherein the optical contrast corresponds at leastto a grey scale of 4 according to DIN EN 20105-A02.
 8. The methodaccording to claim 6, wherein the lower layer is colored and the colorof the lower layer is in optical contrast to a color of the upper layer.9. The method according to claim 6, wherein said performing is carriedout by measuring the optical contrast in accordance with DIN EN ISO11664-4 using a spectrophotometer and detecting a visual signal.
 10. Themethod according to claim 1, wherein the upper layer and the lower layereach, independently, comprise a polymer material.
 11. The methodaccording to claim 10, wherein the upper layer is a polyamide mouldingcompound applied by extrusion.
 12. The method according to claim 1,wherein the at least two-layer covering further comprises at least onelayer between the metal pipe and the lower layer.
 13. The methodaccording to claim 12, wherein the at least one layer is selected fromthe group consisting of a ceramic layer, a priming layer, an adhesionpromoting layer and a textile reinforcement.
 14. The method according toclaim 13, wherein the at least one layer comprises a priming layer,which is an epoxy resin or a water-based mixture of an epoxy resin and apolyacrylate latex.
 15. The method according to claim 13, wherein the atleast one layer comprises an adhesion promoting layer, which is apolyamide hot-melt adhesive or a polyolefin having functional groups.16. The method according to claim 13, wherein the at least one layercomprises a textile reinforcement, which is a woven fabric or mat. 17.The method according to claim 1, wherein the metal pipe is made of ametal material selected from the group consisting of steel, stainlesssteel, copper, aluminium, cast iron, zinc, a copper alloy, an aluminumalloy, a zinc alloy, brass, galvanized steel, cadmium-coated steel,aluminium-coated metal, and steel coated with a metal alloy.
 18. Themethod according to claim 1, wherein the covered metal pipe is comprisedwithin an offshore wind power plant, an offshore drilling rig, or alighthouse.
 19. The method according to claim 1, wherein the lower layerdirectly contacts the metal pipe.